The embodiments herein relate to methods of designing an invert emulsion fluid having high associative stability.
Hydrocarbon producing wells are typically formed by drilling a wellbore into a subterranean formation. A drilling fluid is circulated through a drill bit within the wellbore as the wellbore is being drilled. The drilling fluid is circulated back to the surface of the wellbore with drilling cuttings for removal from the wellbore. Such drilling fluids may be invert emulsions. An emulsion is a fluid including an internal phase of dispersed immiscible liquid droplets in an external, continuous liquid phase. An invert emulsion, also referred to as a water-in-oil emulsion, comprises an internal phase of water droplets and an external phase of oil. As used herein, the “water” in an invert emulsion refers to an aqueous base fluid and the “oil” refers to any non-polar organic liquid (e.g., petroleum, kerosene, synthetic oil, paraffin, mineral oil, and the like). Invert emulsions for use as drilling fluids may provide superior rheological, filtration, and oil-wetting characteristics. Additionally, invert emulsions may remain stable under extreme subterranean conditions, such as in the presence of high electrolyte concentrations, soluble gasses, high temperatures, and high pressures.
Invert emulsion drilling fluids often comprise particulates therein, referred to as a particulates fraction in the invert emulsion. These particulates may serve to, for example, increase the density of the drilling fluid (e.g., weighting agents, such as barite) to balance pressure and stabilize the wellbore. Other particulates may include corrosion inhibitors, flocculants, fluid loss agents, and the like. The particulates may experience sag within the invert emulsion drilling fluids, which may adversely affect the performance of the drilling fluid. As used herein, the term “sag” refers to a variation in drilling fluid density along a fluid column (e.g., when the fluid is within a wellbore) that is the result of settling of particulates within the drilling fluid. Sag generally results from the inability of the drilling fluid, under the particular conditions of the subterranean formation, to provide adequate suspension properties. Drilling fluids may exhibit sag in both static and dynamic conditions. As used herein, the term “static” refers to a complete quiescent state of the drilling fluid, and the term “dynamic” refers to any situation in which the drilling fluid is exposed to a shear stress (e.g., during drilling).
Sag may result in the formation of a bed of particulates (e.g., weighting agents) on the bottom, or low, side of a wellbore, whether the wellbore is vertical or non-vertical. In some cases, sag may adversely affect a drilling operation, leading to problems including, but not limited to, stuck drill pipe, inability to reinitiate or maintain proper circulation of the drilling fluid, disproportionate removal from a wellbore of lighter components of the drilling fluid, and the like. In some extreme cases, sag may lead to abandonment of a wellbore.